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9
Figure 2-16 Figure 2-17 Figure 2-18 Figure 2-19
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The diagonal is a prism that diverts the light at a right angle to the light path of
the refractor. This allows you to observe in a position that is more comfortable
than if you had to look straight through. This diagonal is an erect image model
that corrects the image to be right side up and oriented correctly left-to-right
which is much easier to use for terrestrial observing. Also, the diagonal can be
rotated to any position which is most favorable for you. To install the diagonal
and eyepieces:
1. Insert the small barrel of the diagonal into the 1.25” eyepiece adapter of the
focus tube on the refractor – Figure 2-20. Make sure the two thumbscrews
on the eyepiece adapter do not protrude into the focuser tube before
installation and the plug up cap is removed from the eyepiece adapter.
2. Put the chrome barrel end of one of the eyepieces into the diagonal and
tighten the thumb screw. Again, when doing this make sure the thumb
screw is not protruding into the diagonal before inserting the eyepiece.
3. The eyepieces can be changed to other focal lengths by reversing the
procedure in step 2 above.
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The eyepiece (or ocular) is an optical element that magnifies the image focused by
the telescope. Without the eyepiece it would be impossible to use the telescope
visually. Eyepieces are commonly referred to by focal length and barrel diameter.
The longer focal length (i.e., the larger the number) the lower the eyepiece
magnification (i.e., power). Generally, you will use low-to-moderate power when
viewing. For more information on how to determine power, see the section on
“Calculating Magnification”. The eyepiece fits directly into the focuser of the
Newtonian. To attach the eyepieces:
1. Make sure the thumbscrews are not protruding into the focuser tube. Then,
insert the chrome barrel of the eyepieces into the focus tube (remove the
plug up cap of the focuser first) and tighten the thumbscrews – see
Figure 2-21.
2. The 20mm eyepiece is called an erecting eyepiece since it corrects the
image so it is right side up and corrected left to right. This makes the
telescope useful for terrestrial viewing.
3. The eyepieces can be changed by reversing the procedure as described
above.
Figure 2-20
Figure 2-21
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